Keeping it working

1. The filter, monthly to seasonally

This is the one that matters. A clogged filter starves the coil of airflow, which does three things at once: extraction drops sharply, the coil runs colder than designed and can ice, and the machine keeps drawing its full power throughout. Efficiency collapses without the wattage falling at all.

Most filters on household units are washable rather than consumable. Pull it, rinse it under a tap, let it dry completely, and refit it - a wet filter refitted immediately is worse than a dusty one. Several units flag this for you: the GE has a clean-filter alert and the Honeywell TP70 has a filter-change alert, which are among the more useful features in the category precisely because nobody remembers otherwise.

2. The tank, whenever you use it

Standing condensate in a warm room grows biofilm and eventually smells. If the machine runs on its bucket, rinse the tank when you empty it and wash it properly a few times a season. If it runs on a hose, the tank sits dry and this is not an issue - one of several quiet advantages of continuous drainage.

Do not put bleach in the tank as routine maintenance. It is unnecessary at these timescales, and on some machines it will sit against plastics and seals that were not chosen with it in mind.

3. The drain line, once a season

Condensate is fairly clean water, but a hose that has sat in a damp basement for a season can grow a biofilm plug, usually at a narrow section or a join. That plug is the cause of a slow-draining line and, eventually, of water on the floor.

Disconnect the hose, run water through it from a tap, and refit it. Two minutes. While it is off, check the route for a sag that has developed as the hose settled - that is the other thing that appears over a season rather than immediately. Drain not working.

4. The coil, annually

Dust that gets past the filter settles on the evaporator fins and insulates them, which reduces extraction the same way a clogged filter does. Once a year, unplug the machine, take the front off if it comes off easily, and look.

If the fins are dusty, a soft brush and a vacuum will clear them. Two rules: brush along the fins rather than across them, and never poke anything metal between them. The fins are thin aluminum with refrigerant tubing behind, and a puncture is a scrapped machine rather than a repair.

What is not owner-maintainable

• Anything inside the sealed refrigerant circuit. Recovery equipment and certification are required to open it legally and safely.
• The compressor itself. Not serviceable in a household portable.
• Electronic controls beyond a reset. Unplugging for a few minutes clears a confused controller and is worth trying; beyond that it is a warranty question.

Warranty terms vary more than you would expect: most portables here publish one year, while AlorAir publishes a six-year limited warranty on its crawl space units. For a machine that lives somewhere nobody visits, that difference is a real part of the value.